1. Field of the Invention
The invention relates to a self-amplifying electromechanical partial lining disc brake. The term “partial lining” means that the disc brake, in particular its friction brake pad, extends over a fraction of a circumference of a brake disc. Usually, the partial lining disc brake, its brake caliper, and the friction brake pad or pads are situated at a location on a circumference of the brake disc and extend over only a short distance of its circumference in the circumferential direction.
2. Description of the Prior Art
US Publication No. 20070137949A1 has disclosed a self-amplifying electromechanical partial lining disc brake of this kind. The known partial lining disc brake has a movable friction brake pad that an electromechanical actuating device can press against a brake disc in order to actuate the partial lining disc brake. The electromechanical actuating device has an electric motor, a mechanical reduction gear, and a rack-and-pinion transmission for converting the rotating motion of the electric motor and reduction gear into a translating motion for moving the friction brake pad. There are also other conceivable and possible embodiments of the electromechanical actuating device; for example, the rotating motion can be converted into a translating motion by means of a screw drive or a cam.
The known partial lining disc brake has a self-amplification device with a ramp mechanism. The ramp mechanism has three ramps that support the friction brake pad at three points that do not lie on a straight line. The support can be thought of as a three-point support at the corners of an imaginary triangle. The support is statically determined. The ramps extend in a circumference direction and at a ramp angle to the brake disc. In lieu of extending in the circumference direction, the ramps can also extend, for example, in the direction of a chord in relation to the brake disc. The essential thing is for there to be a path of the ramps and a movement of the friction brake pad such that a friction force, which the rotating brake disc exerts on the friction brake pad which is pressed against the brake disc during braking, acts on the friction brake pad in the direction of a narrowing wedge gap between the ramps and the brake disc in order to produce the self-amplification described below. The ramp mechanism movably guides the friction brake pad in the circumferential direction in relation to the brake disc and at the ramp angle in relation to the brake disc. The electromechanical actuating device produces the movement of the friction brake pad for the actuation of the partial lining disc brake. The ramp angle can change in the course of the ramps. For example, a large ramp angle at the beginning of the movement of the friction brake pad makes it possible to quickly overcome an air gap, i.e. a gap between the friction brake pad and the brake disc, at the beginning of the actuation of the partial lining disc brake, in order to quickly bring the friction brake pad into contact with the brake disc. A ramp angle that becomes increasingly smaller with the movement of the friction brake pad achieves a more powerful self-amplification as the braking force increases. If the ramp angle is constant over the course of the ramps, this is also referred to as a wedge mechanism. The movement of the friction brake pad is a helical movement in the circumference direction of the brake disc, with a changing or constant slope in relation to the brake disc.
When the partial lining brake disc is actuated, the rotating brake disc exerts a friction force on the friction brake pad that is pressed against it. The friction force acts on the friction brake pad in the direction of a narrowing wedge gap between the ramps and the brake disc. Because of the ramp angle and due to the so-called wedge principle, the support of the friction brake pad against the ramps produces a supporting force that has a force component perpendicular to the brake disc. This force component produces a pressing force that presses the friction brake pad against the brake disc. This pressing force results from the friction force; it is not exerted by the actuating device, but presses the friction brake pad against the brake disc in addition to a pressing force exerted by the actuating device. This amplifies the braking force; the partial lining disc brake has a self-amplification; and the ramp mechanism constitutes a self-amplification device that converts the friction force, which the brake disc exerts on the friction brake pad that is pressed against it, into a pressing force.
The ramp mechanism of the known partial lining disc brake has a roller elements that roll along the ramps and support the friction brake pad. The roller elements of the known partial lining disc brake are rollers, for example cylindrical rollers or conical rollers. It is also possible to use balls as the roller elements. The ramps can be raised and/or recessed, for example in the form of grooves or flutes whose depth changes in one direction over the span of their length. The roller elements are situated at the corners of an imaginary triangle.